Researchers Confirm: 'Light at Night' Linked to Cancer

Researchers confirm link between "light at night" pollution and elevated rates of breast cancer. Best bet, they say: learn to sleep in the dark.

Chana Ya'ar, 19/01/11 12:37 | updated: 13:11

Sleeping child

Israel news photo: Alessandro Zangrilli / Wik

Researchers have confirmed a link between "light at night" pollution and elevated rates of breast cancer and prostate cancer.

The news comes in the wake of a report published from a 10-year study conducted by the University of Haifa's Biology Department that found that higher-intensity light during sleep can be dangerous. The study, which found a connection between cancer and artificial lighting, adds its voice to those of previous studies that resulted in similar findings.

More than 1,670 Israeli women were involved in the study, which found that those routinely exposed to higher intensity light in their sleeping environment had 22 percent higher odds of developing breast cancer than those who slept in total darkness.

“Bulbs with high-intensity light contribute more to environmental light pollution, and lead to cancer, we found,” said researcher Professor Avraham Haim.

The researchers theorized that LAN (light at night) harms production of melatonin, a hormone that is released from the pineal gland during the dark part of the 24th cycle and which is linked to the body's night-day cycle of activity and seasonality. Melatonin modulates endogenous estrogen levels.

When the hormone is suppressed, the occurrence of cancer rises, according to the researchers, who published their report in the February issue of Chronobiology International.

Prior Evidence of Link to Cancer
Earlier studies in which Haim participated have shown that people living in areas with more night-time lighting are more susceptible to prostate cancer in men and breast cancer in women. A previous, related study published in September by Prof. Haim also demonstrated a link between suppression of melatonin and elevated rates of the disease.

Cancerous growths in mice exposed to “short days” were smallest, and mice exposed to the interval of LAN during dark hours had larger growths. Those exposed to “long days” had the largest growths.

The study also found that suppression of melatonin definitely influenced development of tumors: mice exposed to “long days” but treated with the hormone exhibited tumors the size of those exposed to “short days.” The death rate in mice treated with melatonin was significantly lower than in those not treated, researchers said.

“Exposure to LAN disrupts our biological clock and affects the cyclical rhythm that has developed over hundreds of millions of evolutionary years that were devoid of LAN,” said the researchers. “Light pollution as an environmental problem is gaining awareness around the world.”

The World Health Organization's International Agency for Research on Cancer (IARC) has already classified working the night shift as a higher grade of cancer risk, the researchers added.